Nitrocellulose coating composition and film made therefrom



Patented Apr. 23, 1929.

, .-UNITED STATES PATENT OFFICE.

I IAUBICE VALENTINE HITT, OI PARLIN, NEW' JERSEY, ASSIGNOR TO E. I/DU PON'J. DE

NEMOURS & COMPANY, OF WILMINGTON, DELAWARE, A CORPORATION OF DELA- WARE;

NITROCELLULOSE COATING COMPOSITION AND FILM MADE THEREFROH;

No Drawing.

This invention relates to coating compocompositions containing solvent softeners,

. particularly nitrocellulose having a certain specific viscosity characteristic. Another object of the invention is to provide such compositions wherein the content of total solids, exclusive of pigments, is more than and the nitrocellulose content more than 7% after the composition has been thinned down to a viscosity between 100 and 300 centipoises as measured by the Stormer viscome-- ter at 28 C. A further object is to properly proportion the ingredients of the compositions, particularly in reference to the pigments, in. order to obtain the most advantageous results. A still further object is to provide films and articles coated with films from the aforesaid compositions, which films shall be hard, durable, tough, adhesive, 30 and non-shrinking. Further objects will be apparent as the following description procoeds.

In the manufacture of pyroxylin lacquers and enamels as heretofore carried on, ithas not be practicable to make solutions having a nitrocellulose content, after thinning to the extent required for use as a, dip or spray lacquer, namely, 100-300 centipoises, of more than about 6%, for with ordinary nitro- 10 cellulose, more than this proportion thereof renders the solution too viscous. Moreover in the presence of this maximum amount of nitrocellulose the proportion of '-gum had to be comparatively low, so that as a rule it has been necessary to limit the total solids content of these old lacquersand enamels, exclusive of pigment, when thinned to'spraying viscosity, namely 100- 300 centipoises, to less than 13%. t

Application filed October 13, 1923. Serial No. 668,285. A

In connection with the compositions of my invention I have found. that by using reduced-viscosity nitrocellulose, which may be produced, for example, as described in the application of E. C. Pitman, Serial No. 594,994 filed October 16, 1922, lacquers and enamels may be prepared having a nitrocellulose content, based on the Weight of the coating composition, exclusive of pigment, and after the required thinning to between 100 and 300 centipoises, of more than 7%, and, if desired above 9%, and a total solids content, exclusive of pigment above 15%. The main advantage attending the use of a high nitrocellulose, high total solids lacquer or enamel of this kind is that the number of coats which it is necessary to apply to form a coating of the desired thickness is materially reduced.

The description of the nitrocellulose content and total solids content as being determined after the required thinning to from 100 to 300 centipoises, is made necessary because of the fact that pyroxylin lacquers are sometimes made and sold in a concentrated form, that is, with a relatively high nitrocellulose content and high total solids content, but with a viscosity so high that the lacquer must be thinned or diluted with a volatile solvent to reduce the viscosity to the required value. When such old concentrated lacquers of the prior art have been thinned down to a Working consistency they have, as explained above, a nitrocellulose content substantially less than 7%, and a total solids content substantially less than 15%. In discussing solutions of cellulose esters, 'etc., it is customary to indicate the concentration of the solution by reference to the number of ounces of cellulose ester, etc, dissolved in one gallon of solvent. For example, a solution obtained by dissolving 16 ounces of nitrocellulose in one gallon of ethyl acetate would be described asa 16 oze ethyl acetate solution of nitrocellulose. I

The ordinary types of pyroxylin lacquers and enamels heretofore known do not contain a solvent softener- This is uite natural in'view of the fact that pryoxy in lacquers hitherto have been chiefly used for forming very thin films, and there has been less reason why a softener should be used. Furthermore, solvent softeners do not exhibit any special advantages in high viscosity nitrocellulose compositions. The new lacquers and enamels, on the other hand, made from reduced-viscosity nitrocellulose, are intended to enter an entirely new field in a new capacity-namely, as competitors of varnish and enamel paint. They will be used to form a comparatively thick coat on nearly rigid surfaces, and this coat must have sufficient flexibility to withstand ordinary blows and slight bending without cracking. This flexibility is attained by the use of a solvent softener.

It is probably still more important that a solventsoftener be present because of the nature of the film made by reduced viscosity nitrocellulose. A solvent softener is important in solutions of reduced viscosity, such as those with which the present invention is concerned, because when the viscosity has been reduced to this degree the film more readily becomes brittle on aging, especially at elevated temperatures. Apparently the reduced viscosity nitrocellulose has less power to retain a non-solvent softener or even a solvent of high volatility, as compared with the ordinary type of pyroxylin which has hitherto been used. By using a solvent softener, and especially one that is substantially non-volatile, the original quality of the film is improved and its life is greatly prolonged. This effect is shown very definitely by tests on aging at 65 C. The use of acetyl-laurin, for instance, makes it possible to stamp the surface satisfactorily even after high temperature storage.

The advantages attending the use of a sol vent softener in the new lacquers and enamels, as compared with the use of a non-solvent softener such as castor oil, comprise the great and unexpected improvement in flexibility of the film, better adhesion, freedom from blushing, ease of sanding and bufiing, etc. Whereas low viscosity nitrocellulose of the herein described type will not provide a flexible film, yet the addition of a solvent softener will not only remove the brittleness by providing a film whose flexibility is large.- ly retained, but it will also provide a material increase in the final flexibility of the film as compared with the original nitrocellulose itself. In this manner, the original low viscosity nitrocellulose is made available for all forms of lacquers and enamels where flexibility is required, whereas previously such low viscosity solutions had a more limited use even with the presence of a softener like castor oil.

As solvent softeners, I may use, for example, any one or more of the following substances: dibutyl phthalate, benzyl butyl phthalate (specifically the ortho-phthalates), acetyl-laurin (see G. L. Schwartz application Serial No. 551,734), camphor, and tricresyl phosphate and their equivalents.

Alnong solvent softeners I prefer to use those which are substantially non-volatile, and for that reason dibutyl phthalate is not as good as. the others mentioned because its volatility is too high in some cases. I-Iow-. ever, if it is used in connection with a practicall nonvolatile softener it is usually very satis aetory. By the term solvent softeners I mean such substances as I have just recited and their equivalents, and preferably such as are liquid below 50 C. and have an appreciable solvent action on pyroxylin.

The following examples are illustrative of my invention, which is not, of course, limited thereto since many changes can be made therein without departing from the spirit and scope of the invention.

EXAMPLE 1.

A lacquer made in accordance with my invention may have the following composition, (the nitrocellulose used in this example having a viscosity, as measured in the form of a 16 oz. C. P. ethyl acetate solution thereof at 28 0., of between 550 and 1500 centipoises) Lacquer #1.

Per cent.

Nitrocellulose of reduced viscosity--- 12.75 Butyl acetate 20.25 Butyl alcohol 8.70 Ethyl acetate 10.50 Denatured alcohol 10.00 Acetone 6.70 Methyl alcohol 4.80 Resin or gum A 5.40 Toluol 12.00 Acetyl laurin 2.00

1100 centipoises. WVhen thinned by adding 40 parts of thinner to 60 parts of lacquer its viscosity is between 100 and 300 centipoises.

Per cent.

Ethyl acetate 25 Butyl acetate 25 Butyl alcohol 1O Toluol 20 I Xylol 20 The thinner used may have the following composition In preparing this lacquer #1, the 'following procedure may be followed, although the lacquer may also be prepared in various I other ways Seventy-five parts by weight of a nitrocellulose base solution (a), containing a'reo duced viscosity nitrocellulose whose v scosity lies between 500 and" 1500 cent'ipoises in lowing composition Percent. Butyl acetate .35 Butyl alcohol -1l Ethyl acetate 12- 2-B denatured. alcohol -16; -Acetone f -Methy'l alcohol 6 Pyroxylin 17 Total 100 16 oz. GJP. ethyl acetate solution, is mixed with thirteen parts by weight of a resin solution to give the necessary resin contentas shown above. Softener and toluol are added and thefiwhole mixed until thorough incorporation is produced. A clear dark amber colored solution should be produced.

Thenitrocellulose base solution referred to in the preceding paragraph has the fol- An ordinary barrel type of. mixture is used in making up this solution. The nitrocotton, having a viscosity of about 35,000 centipoises, plus .8% of its weight of crystalline sodium acetate is added to the mixer,

care being taken that there is a thorough intermixmg of the salt and Intro-cotton.

The solvents are then added, and the Whole thoroughly mixed until an easily" flowing so- ;Ilution is obtained. This solution is then run into barrels which are placed in a closed room maintained at 38.410 0. Samples are taken from these barrels from time to time andv viscosity measurements make until the dif fci'ence between separate viscosity measuremcnts indicates that the reducing action has practically ceased. This has been found by experience to require about four to six weeks for this type of mixture. -VVhen this pointv is reached the'barrels are withdrawn from the heat-ed room and stored atord nary room temperature until such time as the contents are needed for use in regular mix- 'tures. -The nitrocellulose component of the reduced viscosity solution, when 1solated, and

I dissolved in C. P. ethyl acetate, forms a solution having a viscosity of about 600 to 700 centipoises at 28 C.

Theresin solution may be prepared in the usual Way by dissolving the resin to be used (e. g. dammar, shellac, or elemi) in a solvent mixture in which it dissolves readily, and which mixes readily with (the nitrocellulose base solution, and separating the clear solution by. decan-tation after the insoluble portionihas-zsettled.

EXAMPLE 2.

' -Another typical lacquer coming within the scope oi my invention has'the following compos tion:

.The viscosity of the above described lacquer No.2 as measured by. the Stormer viscometerat 28 C. is between 1300 and 1500 centipoises. When thinned by adding 40 parts of tninner to 60 parts of lacquer the viscosity is between '100 and 300 centipoises g In the above described lacquer .'#2 there may be used for the resin constituent any of the resins or gums mentioned above; and

in place of dibutyl phthalate, other solvent softeners may be used.

The pyroxylin used, in lacquer #2 has an average viscosity'below 400 centipoises, and,

preferably of about 800 centipoises. This low average viscosity pyroxlyn is prepared by mixing twenty-one.(2l) parts by weight of the nitrocellulose base solution (a) described in connection with lacquer #1 '(said base solution'containing 17% of nitrocellulose having a viscosity of'about 625 centipoises), with about forty-nine (49) parts of a base solution-(b) of practically the same solvent composition as base solution (a) but containing. 30% of nitrocellulose whose 16 oz. C. P. ethyl" acetate solution has a viscosity of'about centipoiscs.

'A nitrocellulose base solution (7)), containing nitrocellulose whose 16 oz. C. P.

ethyl acetate solution has a viscosity of-between-90 and 340 centipoises when measured by the Stormer viscometer. at .28? C., may

be produced-by dissolving? in asolvent com-- position a soluble nitro-cotton whose 16 oz. C. P. ethyl acetate solution has a viscosity of about 35000 centipoises at 28 (3.,tofform a. solution having the following composilion:

Per cent. Butyl acetate 33. 30 Butyl alcohol 5.70 Acetone, C. 1 2.30

Ethyl acetate .11. 30 Per cent. Methyl alcohol, (09%) 5. 10 Pigment 9.00 2B denatured alcohol 12. 00 :Py1'0Xy1lll} 10. 5'0 Nitrocellulose 30.00 Resinor gum 7.60 Dibutyl phthalate -1 6. 100.00 Butyl acetate 21.60 and subjecting the nitro-cottonin this solut alcohol-c tion to the action of sodium acetate. 7 The Ethyl t detailed procedure for making base solution Denatured -9 (b) is exactly similar to that described above A for making base solution (0.), except that Methyl 90 the sodium acetate added is equal to 2% of BenzoL 40 the weight of the nitrocotton used. The time necessary to obtain'the required reduc-- 00 tion in viscosity is 3840 C. i

To manufacture the lacquer, the following procedure is followed:

Forty-nine parts by 'weight'of the 3% base, and twenty-one parts by weight of we 17% base are mixed with twelve and one-- half parts by weight of a resin solution, and the necessary amounts of :dibutyl phthala'te and toluol added. The whole-is mixed until. a clear dark amber solution is obtained, and

Althouglrthe viscosity of my new coating compositions when ready for use as dip or spray lacquers or enamels, 1s from about 100 to '390 centipoises, I preferably'employ a nitrocellulose 'whose viscosity-characteristic is such that theafinished-coating composition""willthave a viscosity of about 125 c-entipoises, the nitrocellulose content being sive of pigment, above Where an enamel i'sto be prepared a pig'- ment isinoorpora'ted in the coating compo sition-,-'l the fl peroentage 'of pigment belng' usually between '5' and 30%- based upon the weight ofthe finished enamel. suitable two to three weeks at eral pigments and lakes in. general may be. used. A typical enamel illustrative of my invention has the following composition, the viscosity of the nitrocellulose used therein beingbetween 400 and 1500 centipoises in 16 oz. ethyl acetate solution:

This enamel will show a viscosity inthe neighborhood of 1,000 centipoises'and will have to be thinned in the neighborhood, of

30% of thinner and 70% of enamel to ob-.

tain spraying viscosity.

The volatile solvents employed in these high percentage pyroxylin, low viscosity coating I compositions are chiefly acetone, acetone oils, the lower alcohols (methyl, ethyl, etc.) and the lower alkyl acetates, such as ethyl, .propyl, butyl, and amyl acetates. As d-iluents there may be used the volatile petroleum hydrocarbons, and thebe'nzenoid hydrocarbons such, for example, as benzene and toluene. I have found it advantageous to employ low boiling alcohols and certain high boiling esters or ketones, such as butyl acetate, in approximately the proportions described; that is, the low boiling alcohols approximately in the same proportion as the nitr ocellulose., and the high boiling esters or ketones approximately from an equal proportion to about three times the proportion of nitrocellulose. I-have found it advantageous'to have the proportion of resin or gum in many cases approximately'two-thirdsto one-half that of the nitrocellulose and the solvent softener approximately one-third to one-seventh that of the nitrocellulose as shown by the foregoing examples, although some deviation may be made from these proportions, The proportion of pigment will vary from 5 to 30% as stated previously, according to the natureof the lacquer or enamel desired to be produced, and the quality of pigment; as shown by-the examare the values of a 16-oz. chemicallypure ethylacetate solution thereof. The viscosity characteristic of the nitrocellulose emploved in the foregoing compositions should be .below' 1500 centipoises when employing low viscosity nitrocellulose, and will often preferably be below 400 centipoises. In View of the favorable action of sodium acetate or its equivalents in reducing the viscosity of nitrocellulose, asherein described, there will be no disintegration thereof so as to reduce the. nitrogen content to too low a figure, and it is therefore unnecessary to specify a lower value for the viscosity characteristic, but such may be well below 400 or eren 100 centipoises.

The films produced from the lacquers and enamels described above will be hard, durable, tough, adhesive, and relatively nonshrinking. The films will, as before stated, be used to form relatively thick coats on rigid surfaces, and owing to the presence of solvent softeners, they will have good flexibility and the non-softeners will reinforce the low viscosity nitrocellulose (which is relatively very low), so that both materials will cooperate in providing a film which will not become brittle on aging and not shown by a low viscosity film containing no solvent softener. The presence of resins also materially enhances the quality and adhesion of the films, and thus, in conjunction with the solvent softeners, provides a film not heretofore produced. By the addition of pigments in the relative proportions described, a successful colored film may be produced.

' As many apparently widely difierent embodiments of this invention may be made without department from the spirit thereof,

it is to be understood that I do not intend to A limit myself to the specific embodiments thereof except as indicated in the appended claims.

I claim 1. A nitrocellulose coating composition comprising in combination nitrocellulose whose viscosity characteristic is such that a 16-02. C. P. ethyl acetate solution thereof has a viscosity at 28 C. of below 1500 centipoises; and a solvent softener for the nitrocellulose.

2. A'I11bI0C8lll1lOS6 coating composition comprising in combination nitrocellulose whose viscosity characteristic is such that a 10-oz. C. P. ethyl acetate solution thereofhas a-viscosity at 28 C. of below 400 centipoises; and a solvent softener for the nitrocellulose.

3. A nitrocellulose coating composition comprising in combination a reduced viscosity nitrocellulose whose viscosity characteristic is such that a 16-02. C. P. ethyl acetate solution thereof has a viscosity at 28 point below 50 C. and. being non-volatile. I

4. A pyroxylin coating composition having a viscosity of between 100 and 300 centipoises at 28 0., and containing more than 9% of nitrocellulose, a volatile nitrocellulose-solvent, and a solventvsoftener for the nitrocellulose, the viscosity-characteristie of said'nitrocellulose being such that a 16-02. C. P. ethyl acetate solution thereof has a viscosity at 28 C. of less than'1500 centipoises.

5. A pyroxylin lacquer comprising, in combination, nitrocellulose, a substantially non-volatile solvent softener therefor, and a gum, said nitrocellulose having a viscosity characteristic which, when expressed in terms of the. viscosity'of a 16 oz. 0. Rethyl acetate solution thereof, is less than 1500 centipoises.

6. A lacquer the softener comprisesdibutyl phthalate.

7. A pyroxylin enamel comprising nitrocellulose, a solvent softener therefor, a pigment, and a gum, the viscosity-characteris-.

tic of the nitrocellulose, expressed in terms of the viscosity of a 16 oz. ethylacetate soalcohol in about the same proportion as the nitrocellulose.

10. A coating composition comprising a low viscosity nitrocellulose having aviscosity characteristic below 1500 centipoises as defined; a solvent softener in the proportion of about one-seventh to two-thirds that of the nitrocellulose; a resin less than one-half the proportion of the nitrocellulose; a low boilas defined in claim 2 in which show such signs of deterioration as might be lution thereof,.being below 400 centipoises.

ing alcohol in about the same proportion as the nitrocellulose; and a high boiling ketone or ester in a proportion from about one to three times that of the nitrocellulose.

11. A coating composition comprising a low viscosity nitrocellulose having a viscosity I characteristic below 1500 centipoises as defined; a solvent softener from about oneseventh to two-thirds the proportion of the nitrocellulose; and a resin in less than one-.

half the proportion of nitrocellulose.

12. A coating composition comprising a low viscosity nitrocellulose having a viscosity characteristic below 1500 centipoises as defined; a resin, and a pigment; the proportion of the resin being less than half that of the nitrocellulose, and the proportion of pigment being from to 30 parts for about 12 of the nitrocellulose. b

13. A coating composition comprising. a

low viscositynitrocellulose having. a viscosity" characteristic below 1500 centipoises as defined, a resin, a solvent softener, and a pigmentythe proportion of resin being less than'half that of the nitrocellulose, the proportion of softener being from one-seventh to two-thirds that of the. nitrocellulose, and the proportion of pigment being from5 to 30 parts for about 12 of the nitrocellulose,

14. A coating composition comprising a low viscosity nitrocellulose having a viscosity characteristicbelow 1500 centipoises as defined, inthe proportion of about 10 parts;

a resin less than 5 parts; a pigment 5 to 9 parts; a solvent softener from 2' to 7 parts;

, a small proportion of non-drying oil, but

softener.

"viscosity characteristic is below. 1500 ,centi-. po1ses, a resin in the proportion (if less than 21, An article coated with a hard, dur able,

17. An article coated with a hard, durable, tough, adhesive, substantially non-shrinking 4o film containing nitrocellulose whose viscosity characteristic is below 1500 centipoises as defined, a solventsoftener, and a resin.

18. An article coated With a hard, durable, tough, adhesive, substantially non-shrinking film containin nitrocellulose whose viscosity characteristic 1s below 400 centipoises as defined, and a solvent softener.

19. An article coated with a hard, durable, tough, adhesive, substantially non-shrink.- ing film containing nitrocellulose whose viscosity characteristic is below 1500 centipoises, a solvent softener in the proportion of one-seventh to two-thirds that of the nitrocellulose, and a igment in the proportion of 5 to 9' arts or 12 of nitrocellulose. 20. An artic coated with a hard, durable, tough, adhesive, substantially non-shrinkingfilm ."contai'ning nitrocellulose whose half that of the nitrocellulose, and 'a pigment in the proportion of 5 to 9 parts for 12 of nitrocellulose and a solvent softener.

tough, adhesive, substantially non-shrinkfilm containing nitrocellulose Whose viscosity characteristic is below 1500 centipoises, a solvent softener in the; proportion of oneseventh to two-thirds that of the nitrocellulose, a resin in the'proportion of less than half that of the nitrocellulose, and a pigment in the proportion of 5 to 30- parts for 12 of nitrocellulo'se' In testimony whereof I afiix my signature.

MAURICE VALENTINE HITT.

CERTIFICATE OF GORREC'EION.

Patent No. 1,710,453.

was Avril 2a, 1929, a

MAURICE VALENTINE Hm.

'It is hereby certified that error appears in the printed speeiii cation oi th?l above numbered patent requiring correction as follows: Page 1, line 35, ior t e word "be" read "been"; page 3, line 39, for the word mixture read mixer ,m. page-5, line 24, for the compound word "non-softeners read solvent solitenerstfl and that the said LettersPatent should be-read' with these correct ons t erem a the same may conform to the record of the 08801111110 Patent Office. Signed and sealed this 11th day of June, A. D. 1929.

(Seal) M. J. Moore, Acting Commissioner of Patents.

Patent No. 1,71%,453. Gmmed April 23, 1929, to

MAURECE VALENHNE IPHEJ'E.

It is hereby certified that enter appears in the prim-ed speeifieetion 0f the above numbered paeent requiring eorreetiee as ieHeWs; Page 1, line 35, for the Werd "he" need "been"; page 3, fine 3%, fee" the Wfiid "mixture" read "mixefl; page 5, line 24, for the eompeeed Werd "non-sefteners" read "seivent softeners"; and that the said Letters Patent sheuid be read with these eerreetiens therein that the same may cesium to the reeerd e? ease in the Patent @ffiee.

Signed and seabed this we day of Ewe, A. D. 1929.

M. J. Meme,

(Seal) Acting Cemmissiener 0% Patents. 

